Kudos for at least trying to address this, MS should hang their head in shame, this is not the hardest problem to solve these days. If we could do it in 1995 they should be able to do it 30 years later.
7. The absolute brain dead formatting, which makes typing equations or e.g. python exponents super annoying (no I didn't want to have this text bold)
I mean don't get me wrong, I'm not a big fan of teams either, but it's absolutely mind boggling how slack got to such a dominant position in this space
Teams is unjustifiably worse than slack.
The only way you can hold this opinion is if you haven't been forced to use Teams.
I use both on Linux via Firefox (their tabs are pinned side by side). I prefer Teams because:
a) Slack constantly forgets my credentials and i need to go through a whole dance of logging in, proving i'm human by clicking bicycles, having it email some code. Pretty much every day.
b) Slack, for some reason i cannot fathom, randomly switches me to "do not disturb" mode (or something like that) even though i'm right there. Not even away: it switches to a mode where i do not receive notifications when someone messages me. Fortunately it still does the beepy sound and i do keep the tabs visible on my screen all the time so i actually do notice messages, but i had at least a couple of questions from others why i am in that mode.
c) Slack does not support audio calls. Not sure why, but it doesn't work in Firefox. Teams does work just fine. Fortunately all work meetings are done via Teams and all people on Stack are also on Teams so if someone wants an audio call we use Teams, but still, a negative for Slack.
The only issue i had with Teams is that its text input can get confused when typing `backticks` and it seems to dislike using emojis at any place except the end of the text. Also Slack has some (old) meme emojis, though if that is a good thing or not depends on your taste :-P.
My slack experience is old so I don't remember but on msteams there aren't audio calls at all. All calls all video calls, the only difference the audio/video call buttons do is wether your webcam will be activated or not from the beginning but you can still disable it before joining on a video call and you can always activating your camera even if you pressed the telephone looking button to start the call.